IEEE802.21 is in the International standardization stage for media independent handover (MIH) between heterogeneous networks, and is to provide seamless handover and service continuity between heterogeneous networks in order to improve a user's convenience for a mobile terminal. The IEEE802.21 defines basic requirements such as an MIH function, an event service (ES), a command service (CS), and an information service (IS).
The mobile terminal is a multimode node that supports one or more interface types, wherein the interface may be one of the following types: wire-line type such as 802.3 based Ethernet; IEEE802.XX based wireless interface such as IEEE802.11, 802.15, and 802.16; and interface prescribed by a cellular standardization organization such as 3GPP and 3GPP2.
FIG. 1 illustrates a protocol stack of a multimode mobile terminal. As shown in FIG. 1, a multimode mobile terminal has a media access control (MAC) layer and a physical layer (PHY) of each mode, and an MIH function is a logic entity and can freely be arranged while implementing interface through each layer and a service access point (SAP) within a protocol stack.
Media independent handover (MIH) should be defined between 802 based interfaces or between the 802 based interfaces and non-802 based interfaces 3GPP and 3GPP2 mentioned above. A mobility management protocol of an upper layer such as a mobile IP and a session initiation protocol (SIP) should be supported for handover and a seamless service.
Hereinafter, a related art handover between heterogeneous networks will be described.
The IEEE802.21 standard is to assist various handover methods to be easily operated, wherein the handover methods can be classified into “break before make” and “make before break.” The media independent handover function (MIHF) provides an asymmetric service such as a media independent event service (MIES) and a symmetric service such as a media independent command service (MICS) to upper layers and lower layers through a service access point (SAP) which is well defined. The MIH technique includes three MIHF services and a media independent handover protocol. The three MIHF services include a media independent event service (MIES), a media independent command service (MICS), and a media independent information service (MIIS).
The media independent event service is information forwarded from a link layer to upper layers, wherein the upper layers can receive the information through a registration procedure. In this case, in order to assist handover by predicting handover, the upper layers including the mobility management protocol are required to receive link layer information as to that handover will occur soon or handover has been just implemented. The media independent event service can be classified into a link event terminating at the MIHF from an entity that has generated an event in lower layers (second layer and below) and an MIH event forwarded to upper layers (third layer and above) registered by the MIHF. The link event and the MIH event can be classified into two types depending on areas to which they are forwarded. If the events are generated from an event source within a local stack and forwarded from the event source to a local MIHF layer or from the MIHF layer to the upper layers, they are referred to as local events. If the events are generated from a remote event source and forwarded from the remote event source to a remote MIHF layer and then from the remote MIHF layer to the local MIHF layer, these events are referred to as remote events.
FIG. 2 illustrates a structure of a local event model and an MIH event model. The MIH events are forwarded from an MIH layer to a higher management entity or an upper layer, and correspond to event triggers of the related art. The link event is forwarded from the lower layer (MAC or physical layer) to the MIH layer, and primitives are used as the link event, wherein the primitives are used in each interface MAC layer or physical layer.
FIG. 3 illustrates a structure of a remote link event model according to the present invention. If an event is generated from a lower layer within a local stack to the MIH layer within the same local stack, the MIH layer forwards the generated event to the MIH layer of a remote stack. Also, the event may be generated from the lower layer within the remote stack to the MIH layer of the remote stack, whereby the MIH layer of the local stack may receive a trigger.
FIG. 4 illustrates a structure of a remote MIH event model according to the present invention. Referring to FIG. 4, the MIH layer within the local stack generates a remote MIH event and forwards the generated remote MIH event to the other MIH layer within the remote stack. The other MIH layer forwards the remote MIH event to an upper management entity or an upper layer within its stack. Also, the event may be generated from the MIH layer within the remote stack to the MIH layer within the local stack, whereby the upper layer of the local stack may receive a trigger.
The media independent command service corresponds to commands sent from the upper layers (third layer and above) to the lower layers (second layer and below) to allow the upper layers and other MIH users to determine the link status and adjust an optimized operation of a multimode device. Similarly to the media independent event services, the media independent command service is classified into a link command and an MIH command. The link command and the MIH command are classified into a local command and a remote command depending on areas to which they are forwarded. A local MIH command is generated from the upper layers and then forwarded to the MIHF layer (for example, from the mobility management protocol of the upper layer to the MIHF layer or from a policy engine to the MIHF layer). Local link command languages are generated from the MIHF layer to adjust lower layer entities and then forwarded to the lower layers (for example, from the MIHF layer to the media access control layer or from the MIHF layer to the physical layer). A remote MIH command is generated from the upper layers and forwarded to a remote peer stack, and a remote link command is generated from the MIHF layer and forwarded to the lower layers of the remote peer stack.
FIG. 5 illustrates a structure of an MIH command model and a link command model. The MIH command is generated from the upper management entity or the upper layer and then forwarded to the MIH layer, and is to command the MIH layer to take some action. The link command is generated from the MIH layer and then forwarded to the lower layer, and is to command the lower layer to take some action.
FIG. 6 illustrates a structure of a remote MIH command model. The remote MIH command is generated from the upper management entity or the upper layer within the local stack and then forwarded to the MIH layer. The MIH layer forwards the remote MIH command to the other MIH layer within the remote stack. Also, a command may be generated from the upper layer within the remote stack to the MIH layer of the remote stack, whereby the MIH layer of the local stack may receive the command.
FIG. 7 illustrates a structure of a remote link command model. The MIH layer within the local stack generates the remote link command and forwards the generated remote link command to the other MIH layer within the remote stack. The other MIH layer forwards the remote link command to the lower layer within the remote stack. Also, the command may be generated from the MIH layer within the remote stack to the MIH layer within the local stack, whereby the lower layer of the local stack may receive the command.
The media independent information service is for homogeneous or heterogeneous networks within a geographical area. The MIHF layer of the networks as well as the MIHF layer of the mobile terminal can detect and acquire the media independent information service. The media independent information service includes various kinds of information elements required to determine intelligent handover.
The MIH protocol is classified into three stages, i.e., an MIH capability discovery stage, an MIH remote registration stage, and an MIH message exchange stage. The MIH capability discovery stage can be performed by two methods such as a method of broadcasting MIH capability in a network and a method of acquiring MIH capability at the request of a mobile terminal.
Hereinafter, a wireless LAN (IEEE802.11) network structure will be described.
The wireless LAN means a network environment that provides LAN services to a wireless terminal provided with a wireless LAN card, such as PDA and notebook PC, by using an access point (AP) device corresponding to a hub of a wire LAN. In other words, the wireless LAN may be regarded as a system obtained by replacing a wire section between a hub and a user equipment with a wireless section between an AP and a network interface card (NIC) such as a wireless LAN card. Since the wireless LAN does not require a line of a mobile terminal, it has advantages in that it is easy to rearrange the mobile terminal and to construct and extend networks, and enables communication during motion. On the other hand, the wireless LAN has disadvantages in that transmission speed is relatively lower than that of the wire LAN, signal quality is unstable in view of properties of a wireless channel, and signal interference may occur.
FIG. 8 illustrates an example of a network of a wireless LAN. As shown in FIG. 8, the network of the wireless LAN is classified into two types depending on whether the network includes AP. The network of the wireless LAN, which includes AP, is referred to as an infrastructure network while the network of the wireless LAN, which does not include AP, is referred to as an ad-hoc network. A service area provided by one AP is referred to as a basic service area (BSA), and a mobile terminal which includes AP and is connected with the AP is referred to as a basic service set (BSS). A service provided to the mobile terminal connected with the AP is referred to as a station service (SS). The SS includes a service exchanged between mobile terminals in an ad-hoc network.
FIG. 9 illustrates an example of a wireless LAN structure which includes a distribution system (DS) and an extended service set (ESS). The BSS constitutes an extended service set (ESS) which includes several BSSs BSS1 and BSS2. An AP structure which connects the BSSs is referred to as a distribution system (DS). The DS may be provided by various kinds of techniques (for example, wireless LAN and wire LAN). A service provided through the DS is referred to as a distribution system service (DSS), and the AP is operated by a station STA and at the same time provides the DSS to the STA so that the STA accesses the DS. Communication between the BSS and the DS is performed through the AP which is one of elements of the BSS.
A remote request broker (RRB) which is one of elements of the AP of the wireless LAN exists in a system management entity (SME) and enables communication between APs which exist in a mobility domain. In other words, communication through the DS is supported between the APs which own equal mobility domain ID by a logical connection structure through the DS. The RRB generates a remote request/response frame between a current AP and a next candidate AP or relays messages between them.
The wireless LAN (IEEE 802.11) according to the related art has considered a procedure for the AP and the mobile terminal to which MIHF is applied for media independent handover. Also, in the case that the AP which is currently of service to the mobile terminal does not support MIHF, the mobile terminal of the wireless LAN cannot be supported by media independent handover. Moreover, even in the case that the AP supports MIHF, the MIHF of the AP and the mobile terminal remotely transmit and receive MIH messages as general data. For this reason, a problem occurs in that latency is caused.